Office of
United States Ground Water and
^1 Environmental Protection Agency Drinking Water

CLASS V UIC STUDY FACT SHEET
SPECIAL DRAINAGE WELLS
What is a special drainage well?
Hie specific types of Class V underground injection control (UIC) wells that fit into this category are: pump control
valve discharge and potable water tank overflow discharge wells; landslide control wells; swimming pool drainage
wells; and dewatering wells. Pump control valve discharges and potable water tank overflows may be drained to
the subsurface on occasion, usually when an emergency overflow or bypass procedure takes place. Landslide
control wells are used to dewater the subsurface in landslide-prone areas. Swimming pool drainage wells are used
to drain swimming pool water to the subsurface for seasonal maintenance or special repairs. Dewatering wells are
used at construction sites to lower the water table and keep foundation excavation pits dry. Dewatering wells may
also be used at mining sites, where they are known as "connector wells," to drain water from an upper aquifer into a
lower one to facilitate mining activities.
What types of fluids are
injected into special drainage
wells?
Drainage fluids from sources other than direct precipitation. (Wells that receive runoff from direct precipitation are
categorized as storm water drainage wells.)
Do injectate constituents exceed
drinking water standards at the
point of injection?
Injectate characteristics vary among the types of special drainage wells. The injectate from pump control valve
discharge and potable water tank overflows are expected to meet all drinking water standards due to the potable
nature of the water. The quality of injectate in landslide control wells depends on the quality of the ground water
that is being drained to a deeper level in the subsurface. The limited amount of available data indicates that
swimming pool drainage well injectate contains colifonns. In addition, the recommended chemical composition of
swimming pool water includes total dissolved solid (TDS) levels above the secondary drinking water standard.
Available data show that dewatering well injectate typically contains the following constituents above primary
drinking water standards or health advisory levels: turbidity, nitrogen-total ammonia, arsenic, cadmium, cyanide,
lead, molybdenum, nickel, nitrate, and radium-226. Additionally, the following constituents in dewatering well
injectate have been detected above secondary drinking water standards: iron, manganese, TDS, and sulfate.
Measured pH levels are also below the lower end of the secondary drinking water standards range.
What are the characteristics of
the injection zone of a special
drainage well?
Because special drainage wells do not tend to be located in areas with specific geologic characteristics (they are
typically located wherever the need for a certain type of drainage exists), generalizations about the injection zone
characteristics are very limited. In FL, where swimming pool drainage wells and mine dewatering wells are
prevalent, the injection zone is typically karst. In some cases, swimming pool drainage wells inject into saline
aquifers. Landslide control wells and dewatering wells inject into deeper aquifers that can accept large volumes of
fluid from upper aquifers.
Are there any contamination
incidents associated with special
drainage wells?
No contamination incidents have been reported for pump control valve discharge and potable water tank overflow
discharge wells, landslide control wells, swimming pool drainage wells, or dewatering wells.
Are special drainage wells
vulnerable to spills or illicit
discharges?
In general, special drainage wells are not highly vulnerable to spills or illicit discharges. The extent of any potential
contamination caused by dewatering or landslide control wells is highly dependent upon the characteristics of the
construction or mining site or potential landslide location that is being dewatered. Pump control valves and potable
water tanks and swimming pools are not especially vulnerable to spills or illicit discharges.
How many special drainage
wells exist in the United States?
There are 1,944 documented special drainage wells and more than 3,750 special drainage wells estimated to exist in
the United States.
Where are special drainage
wells located within the United
States?
The wells are documented in 13 states, although 97 percent are located in FL (782) and IN (1,102).
How are special drainage wells
regulated in states with the
largest number of this type of
well?
Permit by rule'. ID, IN, OH
Area permit'. FL (single family swimming pools only)
Individual petniiP. AK, FL, OR
Where can I obtain additional
information on special drainage
wells?
For general information, contact the Safe Drinking Water Hotline, toll-free 800-426-4791. The Safe Drinking Water
Hotline is open Monday through Friday, excluding federal holidays, from 9:00 a.m. to 5:30 p.m. Eastern Standard
Time. For technical inquiries, contact Amber Moreen, Underground Injection Control Program, Office of Ground
Water and Drinking Water (mail code 4606), EPA, 401 M Street, SW, Washington, D.C., 20460. Phone: 202-260-
4891. E-mail: moreen.amber(S?epa.gov. The complete Class V UIC Study (EPA/816-R-99-014, September 1999),
which includes a volume addressing special drainage wells (Volume 14), can be found at
http://www.epa.gov/OGWDW/uic/cl5study.html.

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